Systems and methods in accordance with the invention deliver increased efficiency when used with a VCRC engine such as is disclosed in U.S. Pat. No. 6,708,654. Especially advantageous are the realizations applied to the engine in passenger car or light truck use. The value realized is increased efficiency at low power at moderate speeds. This is the average mission for all passenger vehicles and most light trucks. A major objective of the invention is to enhance the efficiency of the VCRC prime mover engine as a device to derive mechanical energy from the heat energy of a burning fuel, with higher efficiency in a lighter weight and smaller configuration than has heretofore been the case; particularly at power demands far less than the engine's maximum. A particular use for this engine is for automobile power. In this application, efficiency at low engine torque at moderate speeds is of prime interest since most of the time an engine used in a passenger automobile operates at approximately 10% or less of its maximum power output at moderate speeds-typically 1,500 to 3,000 revolutions per minute (rpm).